A Low-Profile Broadband Circularly Polarized Pattern Diversity Metasurface-Inspired Antenna

A low-profile broadband circularly polarized (CP) patterndiversity metasurface-inspired antenna is proposed, which can realizethe diversity of broadside and conical patterns while radiating CPwaves. First, based on the theory of characteristic mode analysis (CMA),a metasurface composed of 45 square ring elements arranged in a crossshape is designed. Two sets of four characteristic modes of the proposedmetasurface were found, one of which is related to the broadside patternand the other is related to the conical pattern. In addition, two modes ofthe same set provide the possibility for CP waves. Then, by investigatingthe current distribution of these modes, the optimal excitation positionof a pair of cross-slot is obtained. Finally, two feeding networks aredesigned to excite the broadside and conical patterns of the metasurface,respectively. A processed antenna prototype with a low profile of 0.05 lambda 0(the free-space wavelength at the center frequency) is reported forverifying the design concepts. The measured operating bandwidth of theantenna is 11.6% (4.23-4.75 GHz), which is determined by the operatingbandwidth of the two CP patterns. Within this operating bandwidth, themeasured peak gains are 4.33 dBic (broadside) and 4.28 dBic (conical),respectively. This antenna is suitable for mobile wireless communicationsystems because of its broadband CP characteristics.